The present invention relates to a chuck for rotatable tools, in particular drills, screw taps, etc.
A chuck of this type is disclosed for example in the German patent document DE 40 19 427 C2, in which cooling and/or lubricating medium flows through a central main passage of a chuck sleeve and is supplied into a coaxial and axially connected inner axial passage in the shaft of the tool, through which the lubricant passes over a substantial shaft length into the interior. Several radially extended openings are connected with the inner passage with the tool shaft and open at a peripheral side of a depressed distribution groove of the tool shaft. The tool shaft further has individual longitudinal grooves provided on its outer side. They start from the distributing groove and extend to the cutting edges of the tool, for example of a screw head of a screw tap as a tool. The lubricating medium is therefore guided first through the interior of the tool shaft and then is deviated substantially perpendicularly to the radial openings of the tool shaft. From there, the lubricating medium flows into the peripheral distributing groove in the tool shaft, and from it through the axially extending grooves in the tool shaft forwardly to the cutting edges of the tool. The shaft of the tool is surrounded by the sleeve substantially in the region where the circumferential distributing groove is located and on a short, bordering longitudinal portion. The sleeve is releasably insertable in the central inner receptacle of the chuck sleeve. The axial sleeve length is very short, in particular when compared to the axial length of the tool. First of all, it has the disadvantage that due to the relatively short guiding length, a not sufficient guidance of the inserted tool is provided. Also, first of all it is disadvantageous since the cooling and/or indicating medium which is supplied in the longitudinal direction of the tool at the outer side is slightly whirled when it reaches the end of the sleeve without providing a further supply of the lubricating medium in a longitudinal direction of the tool. The further disadvantage with respect to the guidance of the cooling and/or lubricating medium is that it has first the required guidance centrally through the tool shaft and subsequently a deviation by approximately 90.degree. into the radial distributing openings and then another deviation substantially by 90.degree. from the circumferential distributing groove into the individual longitudinal grooves on the outer side of the tool shaft.
The multiple deviation of the cooling and/lubricating medium and the danger of a whirling at the exit of the sleeve leads to the situation that an insufficient lubrication is provided in the region of the tool cutting grooves. Therefore the desired average quantity lubrication is not provided to the cutting edges of the tool, for example a screw head of a screw tap which constitutes substantially 0.5-5 ml per hour of the cooling/lubricating medium. In order to obtain such a low liquid flow rate, with a low over pressure, it was necessary to operate in the range of 3-5 bar and form a cloud enriched with cooling/lubricating particles. By multiple deviations in the flow course and the thusly formed edges required for it, the cloud can be condensed on the deviations and drops can be formed. As a result, a non-uniform lubrication is obtained, with which in the region of the deviations from the edges a droplet can be abruptly released and is supplied along the outer side of the tool, while during this time mainly no cooling/lubricating medium is guided along the tool. It is also disadvantageous that in the known construction of the tool the lubrication guidance must be adjusted to this specific type. The tool for this purpose must be provided at its end with a central inner lubricating passage, and furthermore the radially oriented openings as well as the peripherally depressed distributing groove and further the longitudinally extending, depressed grooves on the outer side of the tool must be provided. These individual openings and grooves weaken the cross-section of the tool, so that such features can be provided in large tools without negative influence on the strength of the tool. However, in small tools with small cross-sections, such openings and passages which substantially weaken the dimension of the tool are very disadvantageous in view of the strength considerations. In addition, such machining of the tool to provide a corresponding guidance of the cooling and/or lubricating medium is expensive.